In a speech transmission system, the Algebraic Code Excited Linear Prediction (ACELP) is commonly applied to speech coders. The code stream generated by an ACELP-based speech encoder is measured in speech frames. FIG. 1 shows the process of transmitting the input data of each frame. As shown in FIG. 1, the speech encoder at the transmitting end encodes the input data of each frame into a group of parameters. The parameters are generally quantized and then transmitted via a communication channel. The decoder at the receiving end re-synthesizes the received parameters into speech signals, thus implementing transmission of the speech signals.
The parameters of the speech frames generated by the ACELP-based speech coder generally include: spectrum parameter, adaptive codebook parameter, algebraic codebook parameter, pitch lag (also known as Long Time Prediction (LTP) lag), adaptive codebook gain, and algebraic codebook gain. The pitch lag parameter is configured to specify a basic period of a speech signal. Generally, the pitch lag at different time always falls within a certain range.
After the data receiving end receives data frames sent from the data transmitting end, the decoder at the receiving end needs to recover erroneous parameter in the erroneous frame if it is determined that an error or loss occurs (namely, an erroneous frame appears). That is, a new parameter is determined as a corresponding parameter of the frame to reduce deterioration of quality of the decoded speech.
In the prior art, when an erroneous frame appears, three solutions specific to the pitch lag parameter are available, as described below.